It’s still early, but it appears McDonald’s scouting report might be spot-on.

Williams, who was signed to surprising two-year, $3.2 million extension in the offseason, made a mark in the middle during his 12 snaps in Thursday’s preseason opener against Denver.

Williams played into the third quarter and mostly squared off against Broncos starting center Manny Ramirez and backup right guard Phillip Blake. When he wasn’t holding the point against the tandem, he was making several notable plays:

First quarter, 1-10-SF 42 (2:40): Williams showed excellent burst and powered past Ramirez, drawing a blatant holding penalty on a run play to the left side. The hold was so obvious that Williams began clapping even before Ronnie Hillman was tackled for no gain.

The quickness off the snap is likely a nod to 6-foot-1 Williams’ work in the offseason. He said he weighs 305 pounds after dropping 25 pounds since the Super Bowl.

First quarter, 1-20-DEN 48 (2:16): Need some help, Manny? On the next play, Williams was double-teamed by Ramirez and starting left guard Zane Beadles. Quarterback Brock Osweiller scrambled right for a one-yard gain.

First quarter, 2-19-DEN 49 (1:50): Ramirez took on Williams one-on-one and was forcefully shoved back into the pocket. Osweiller completed a seven-yard pass to tight end Virgil Green.

Second quarter, 3-10-SF 38 (8:24): Williams lined up over Blake and bull-rushed him backward, collapsing the pocket. Outside linebacker Dan Skuta got pressure off the right edge and Osweiller stepped up into the mess created by Williams. Skuta got the sack.

It’s a small sample size, but it suggests Williams could be this season’s Alex Boone: A talented college player who went undrafted and blossomed with the 49ers.

Like Williams, Boone has reshaped his once-pudgy body in the NFL and the Niners gave him a surprising extension in 2011, before he excelled at right guard last year in his first season as a starter.

Boone went undrafted because of his well-documented alcohol problems. Why was Williams overlooked?

After fumbling for possibilities, defensive coordinator Vic Fangio said this earlier in training camp: ‘Trust me, he should have been drafted.”